Medical electrodes are devices used to transfer the energy of ionic currents in the body into electrical currents which can be amplified, studied, and used in diagnostics. Medical electrodes permit surface quantification of internal ionic currents, yielding a customarily non-invasive test for a variety of nervous, muscular, ocular, cardiac, and other disorders that might otherwise have required surgical intervention to verify their presence. For instance, heart exams using medical electrodes may produce evidence of diminished myocardium strength and may discriminate between primary heart disorders and neurologically-based disorders in addition to detecting heart problems.
Medical electrodes are required to be easy to use, fairly cheap, disposable (or easily sterilizable). In come cases it is beneficial to use electrodes unique to the task they are to perform. The essential role of the electrode is to provide a sufficient electrical contact between a patient's skin and the apparatus used to measure, record, or monitor activity.
Currently, there are disadvantages associated with medical electrodes that are used for cardiac monitoring of hospital patients. One of the major concerns for ECG electrodes is unanticipated detachment. This is extremely dangerous with patients that are in critical care and need remote monitoring to ensure proper functioning of the heart. Inadvertent detachment usually occurs due to a low adhesive strength of the electrodes.
Another contributing factor to unwanted detachment of the electrode is a detrimental characteristic of the skin surface. For example, for some patients, the surface of their skin may be covered with an abundance of hair that may cause improper attachment of the electrode. In other cases, the surface of the skin may be covered with various forms of dirt which also may cause an insufficient adhesive attachment force. These cases require either shaving the hair or cleaning the surface of the skin which is time and labor consuming for medical personnel. In addition, in some cases, for example, for burn victims shaving and/or cleaning is not an acceptable practice.
Another shortcoming of current electrodes is a problem associated with electrodes removal.
The current medical electrodes usually use an adhesive remover solvent to remove or neutralize the adhesive material which is either pre-formed at the bottom surface of the electrode or has to be applied by hospital personnel in a separate action prior to the electrode being attached to the skin.
A major issue that needs to be attended to is pain which may be experienced by a patient as the electrode is being removed. This factor may either be due to high adhesive strength of the electrode, or to the skin sensitivity, and/or hair on the skin surface or a combination thereof. Removal pain is a usual complaint that medical personnel receive from patients during vital signs monitoring involving the use of medical electrodes.
In addition, large amounts of adhesive material may undesirably leave a sticky residue on the skin.
When the electrode is to be removed, an adhesive remover solvent must be obtained and spread around and underneath the electrode for painless detachment. This process is time consuming and difficult for the medical personnel. Many hospitals do not use these solvents, and merely pull the electrodes from the surface of the skin.
In the search for satisfactory medical electrodes, medical and scientific communities have developed a number of designs currently available in the marketplace as well as presenting various designs in numerous publications and patent literature.
For example, a latex-free conductive adhesive electrode Plia-Cell® is manufactured by ConMed Corporation. The electrode is built with a latex free low-profile soft cloth with a radio-translucent snap in the middle of the electrode. The electrode possesses MRI compatibility and can be maintained for a relatively long period of time on the patient's skin.
The ConMed-Plia-Cell® is a solid gel electrode, which is designed with a conductive hydrogel substitute possessing adhesive properties to attain an improved electro-conductive skin-interface contact. The skin-interface substrate of the ConMed-Plia-Cell® electrodes provides pressure sensitive adhesive properties which enable the electrode to adhere to the skin without the use of tape or other securing mediums customarily used with wet adhesive electrodes. The conductive hydrogel substrate substantially eliminates the need for an electrolyte solution, electrode paste or electrode gel.
One of the biggest challenges however experienced with these electrodes, is a low level of tack they can provide. As a result, high pressure must generally be applied to the skin when the electrode is secured in place on a patient's skin, which is undesirable where the patient has sensitive or burnt skin. Another shortcoming of these electrodes is a noticeable amount of a residue adhesive material left on the skin after the electrode removal.
Another type of electrode used currently is the Invisatrace® Wet Gel ECG Electrode, in which an electrically conductive region is designed as a radio-translucent carbon snap. Wet gel electrodes are usually used for long signals and stable baselines. Electrodes, such as the Invisatrace®, achieve a fast electrical contact due to the rapid “wetting” of the skin.
Since this electrode uses a wet gel, the Clear Neoderm® tape is customarily used in order to secure the electrode in place. The wet gel contains water, thickener, ionic salts, surfactants and bactericide/fungicides. To avoid smearing and to reduce motion artifacts, the gel is usually contained in a sponge.
Single gel layer electrode, such as the Invisatrace® Wet Gel electrode and the ConMed-Plia-Cell® are known to compromise the adhesion of the electrode to the skin resulting in a high noise level in the electrical signal being transmitted.
An UltraStim Multistick® electrode manufactured by Axelgaard Corporation is a solid gel type of electrode available with a MultiStick® 2-layer adhesive gel that eliminates performance problems associated with single layer gels. The addition of an intermediate layer permits improved adhesion and increases the reusability potential of the electrode. These electrodes however are costly, and the removal of the electrodes from the skin remains a disadvantage.
The limitations of current electrodes on the market are quite evident due to patients and hospitals' employees dissatisfaction rating.
A number of medical electrodes issues have been investigated and some solutions have been found for the shortcomings of currently available electrodes. For example, Huigen, et al. in “Investigation into the origin of the noise of surface electrodes,” Medical and Biological Engineering and Computing, Volume 40, Number 3, May 2002, explores the causes of noise while recording biomedical signals with medical electrodes.
This article suggests that increasing the surface area of the electrode will reduce noise and thus will produce a more reliable recording. However, with currently used electrodes, the increase in surface area results in an increase in adhesive in contact with the skin. Removing a larger electrode may be more painful for the patient unless adhesive remover is used.
U.S. Pat. No. 4,706,680 describes a specific adhesive for the medical electrodes that is composed primarily of water and cross-linked polyethylene oxide in a hydrophilic gel.
U.S. Pat. No. 7,252,792 discusses the electrical aspects of medical electrode composition and adhesives to ensure the functional reliability when used to take bio-medical measurements. It is suggested that the electrodes should have uniform conductivities with stable current densities.
U.S. Pat. No. 4,640,289 provides a method to manufacture disposable medical electrodes, and is mainly concerned with the terminal piece which attaches to the ECG lead. The reference discusses the use of electrically conductive adhesive hydrogels instead of conventional electrolyte gels and creams.
U.S. Pat. No. 4,657,023 describes a medical electrode in which the metal terminal is eliminated. In this electrode, an integral centrally located section of the conductive member is directly connected to the ECG lead with a clip.
U.S. Pat. No. 4,842,768 describes a novel electrically conductive gel adhesive. The reference provides examples of a synthesized gel, however, the synthesized gels are not tested for adhesiveness and the reference does not fully address the conductivity issue.
U.S. Pat. No. 5,215,087 proposes a modified design of an electrode with a slightly rounded rectangular shape. The electrode does not have a snap on the connector but uses a tab containing a conductive material. The ECG lead wires are connected to the tab. The electrode uses an adhesive hydrogel made from Acrylic acid and potassium chloride.
U.S. Pat. No. 5,385,679 provides a solid state conductive polymer composition useful in the packaging processes presently required for biomedical electrodes.
U.S. Pat. No. 5,406,945 discloses a disposable biomedical electrode formed with an electrolytic gel which decreases the pain and experienced when tearing hair from the patient's body. The hydrogel material is formed from an aqueous material of polyhydric alcohol. Other materials which reduce discomfort to the patient would include polyethylene oxide based polyamine and sodium chloride.
U.S. Pat. No. 7,346,380 discloses a medical electrode that is suitable for both stimulation and monitoring applications. This medical electrode includes an electrically conductive member capable of being connected to an external electro-medical apparatus. This member is in the form of a pliable sheet formed from a material that comprises organic polymer plasticized with a polyhydric alcohol. The polymerization of acrylic acid and N-vinylpurrolidone is used for the copolymer of the adhesive of this medical electrode.
U.S. Pat. No. 5,961,484 describes a medical electrode which includes an external applicator filled with an adhesive remover. As shown in FIG. 1, the electrode comprises a flexible planar member 10 which faces the skin 12 of a patient, and an electrically conductive member 14 embedded in the planar member 10. Electrical wires are attached between a stud 16 and a medical data acquisition device 18. The electrode includes an electrically conductive adhesive 20 which is placed on the side of the planar member 10 which faces the skin of the patient. The electrically conductive adhesive 20 assures that the electrode remains in place on the patient's skin.
Through holes 22 are formed in multiple locations throughout the planar member 10, and alternatively may be formed through the conductive adhesive 20.
An applicator 24 comprising absorbent dispensing material 26 which contains a solvent or adhesive-neutralizing material is attached on the top of the planar member 10. The dispensing material 26 comprises a sponge or cloth material, or a foam which is saturated with the adhesive-neutralizing solvent. Dispensing material 26 is surrounded partly with a thin flexible plastic layer 28. By applying pressure in the direction of arrow R (shown in FIG. 1) on the top of the applicator 24, a user forces the solvent through the holes 22 toward to interface between the adhesive 20 and the skin 12. In this manner a less painful electrode removal from a patient's skin may be achieved.
This design is costly in its fabrication. In addition, the applicator requires accurate measurements of its mechanics, and the manufacturing process requires additional operations for formation of passages for the adhesive remover through the planar member and the adhesive layer. Additionally, due to its viscosity, the adhesive material cannot maintain the holes in an open configuration. Thus, the passage of the solvent to the electrode-skin interface may be obstructed, thereby undermining the intended functionality of the electrode.
Despite rather extended searches in the area of medical electrodes, there is still a long-lasting need for an ergonomically viable medical electrode which would be reliably attachable to, and yet easily and painlessly removable from skin, as well as being inexpensive to manufacture for convenient use by a medical personnel.